Real-time computer graphics | EPFL Graph Search

Real-time computer graphics or real-time rendering is the sub-field of computer graphics focused on producing and analyzing images in real time. The term can refer to anything from rendering an application's graphical user interface (GUI) to real-time , but is most often used in reference to interactive 3D computer graphics, typically using a graphics processing unit (GPU). One example of this concept is a video game that rapidly renders changing 3D environments to produce an illusion of motion. Computers have been capable of generating 2D images such as simple lines, images and polygons in real time since their invention. However, quickly rendering detailed 3D objects is a daunting task for traditional Von Neumann architecture-based systems. An early workaround to this problem was the use of sprites, 2D images that could imitate 3D graphics. Different techniques for rendering now exist, such as ray-tracing and rasterization. Using these techniques and advanced hardware, computers

Roadmap toward the 10 ps time-of-flight PET challenge

Mathieu Benoit, Edoardo Charbon, Christian Morel, Joao Varela

Since the seventies, positron emission tomography (PET) has become an invaluable medical molecular imaging modality with an unprecedented sensitivity at the picomolar level, especially for cancer diagnosis and the monitoring of its response to therapy. More recently, its combination with x-ray computed tomography (CT) or magnetic resonance (MR) has added high precision anatomic information in fused PET/CT and PET/MR images, thus compensating for the modest intrinsic spatial resolution of PET. Nevertheless, a number of medical challenges call for further improvements in PET sensitivity. These concern in particular new treatment opportunities in the context personalized (also called precision) medicine, such as the need to dynamically track a small number of cells in cancer immunotherapy or stem cells for tissue repair procedures. A better signal-to-noise ratio (SNR) in the image would allow detecting smaller size tumours together with a better staging of the patients, thus increasing the chances of putting cancer in complete remission. Moreover, there is an increasing demand for reducing the radioactive doses injected to the patients without impairing image quality. There are three ways to improve PET scanner sensitivity: improving detector efficiency, increasing geometrical acceptance of the imaging device and pushing the timing performance of the detectors. Currently, some pre-localization of the electron-positron annihilation along a line-of-response (LOR) given by the detection of a pair of annihilation photons is provided by the detection of the time difference between the two photons, also known as the time-of-flight (TOF) difference of the photons, whose accuracy is given by the coincidence time resolution (CTR). A CTR of about 10 picoseconds FWHM will ultimately allow to obtain a direct 3D volume representation of the activity distribution of a positron emitting radiopharmaceutical, at the millimetre level, thus introducing a quantum leap in PET imaging and quantification and fostering more frequent use of C-11 radiopharmaceuticals. The present roadmap article toward the advent of 10 ps TOF-PET addresses the status and current/future challenges along the development of TOF-PET with the objective to reach this mythic 10 ps frontier that will open the door to real-time volume imaging virtually without tomographic inversion. The medical impact and prospects to achieve this technological revolution from the detection and image reconstruction point-of-views, together with a few perspectives beyond the TOF-PET application are discussed.

IOP PUBLISHING LTD2020

Crowds for interactive virtual environments

Branislav Ulicny

Crowds are part of our everyday experience; nevertheless, in virtual worlds they are still relatively rare. In this thesis we explore the challenges of bringing crowds into interactive virtual environments and the possible applications of real-time interactive crowds, for example, in the domains of virtual heritage and training systems. We address several topics including real-time generation of higher-level behaviors, lower-level motion control for many characters, management of variety, integration of crowds into virtual environments, interaction with virtual crowds and authoring of scenarios. In comparison with the other crowd modeling approaches, we focus on more complex behaviors of many agents in dynamic environments with possible user interaction. In our system a crowd is modeled as a collection of individuals which react to the environment, to other agents and to real human participants of the simulation and can have very different behaviors, both for one agent in different situations, and for many agents in the same situation. We emphasize the importance of variety as one of the most distinguishing features of the crowd simulations; we introduce the notion of levels-of-variety. We address as well the question of how to author crowd scenes in an efficient way. We introduce a novel approach to create complex scenes involving thousands of animated individuals in a simple and intuitive way. By employing a brush metaphor, analogous to the tools used in image manipulation programs, we can distribute, modify and control crowd members in real-time with immediate visual feedback. We demonstrate the validity of our behavior simulation approach with several case studies, where we use our crowd system to manage crowd behaviour in a virtual reality training system and virtual heritage reconstruction. The potential of our authoring approach is shown by authoring a scenario of a virtual audience in a theater and a scenario of a pedestrian crowd in a city.

EPFL2005

Digital holographic reflectometry

Ahmet Ata Akatay, Tristan Colomb, Christian Depeursinge, Jonas Kühn, Nicolas Pavillon

Digital holographic microscopy (DHM) is an interferometric technique that allows real-time imaging of the entire complex optical wavefront (amplitude and phase) reflected by or transmitted through a sample. To our knowledge, only the quantitative phase is exploited to measure topography, assuming homogeneous material sample and a single reflection on the surface of the sample. In this paper, dual-wavelength DHM measurements are interpreted using a model of reflected wave propagation through a three-interfaces specimen (2 layers deposited on a semi-infinite layer), to measure simultaneously topography, layer thicknesses and refractive indices of micro- structures. We demonstrate this DHM reflectometry technique by comparing DHM and profilometer measurement of home-made SiO2/Si targets and Secondary Ion Mass Spectrometry (SIMS) sputter craters on specimen including different multiple layers.